santa-driver: Use KAUTH_VNODE_WRITE_DATA instead of KAUTH_FILEOP_CLOS…

…E to catch writes

It turns out that the KAUTH_FILEOP_CLOSE action is not used when the kernel automatically closes file descriptors for exiting processes. Some things, like dd, don't close their file descriptors and let the kernel do it for them which we were previously missing.

Source/santa-driver/SantaDecisionManager.cc

@@ -504,7 +504,8 @@ void SantaDecisionManager::FileOpCallback(
   // Filter out modifications to locations that are definitely
   // not useful or made by santad.
   if (proc_selfpid() != client_pid_ &&
-      !strprefix(path, "/.") && !strprefix(path, "/dev")) {
+      !strprefix(path, "/.") &&
+      !strprefix(path, "/dev")) {
     auto message = NewMessage(nullptr);
     strlcpy(message->path, path, sizeof(message->path));
     if (new_path) strlcpy(message->newpath, new_path, sizeof(message->newpath));
@@ -526,7 +527,9 @@ void SantaDecisionManager::FileOpCallback(
       case KAUTH_FILEOP_DELETE:
         message->action = ACTION_NOTIFY_DELETE;
         break;
-      default: delete message; return;
+      default:
+        delete message;
+        return;
     }
 
     PostToLogQueue(message);
@@ -547,9 +550,6 @@ extern "C" int fileop_scope_callback(
   char *new_path = nullptr;
 
   switch (action) {
-    case KAUTH_FILEOP_CLOSE:
-      if (!(arg2 & KAUTH_FILEOP_CLOSE_MODIFIED)) return KAUTH_RESULT_DEFER;
-    // Intentional fall-through
     case KAUTH_FILEOP_DELETE:
     case KAUTH_FILEOP_EXEC:
       vp = reinterpret_cast<vnode_t>(arg0);
@@ -576,20 +576,31 @@ extern "C" int fileop_scope_callback(
 extern "C" int vnode_scope_callback(
     kauth_cred_t credential, void *idata, kauth_action_t action,
     uintptr_t arg0, uintptr_t arg1, uintptr_t arg2, uintptr_t arg3) {
-  if (action & KAUTH_VNODE_ACCESS ||
-      !(action & KAUTH_VNODE_EXECUTE) ||
-      idata == nullptr) {
+  if (action & KAUTH_VNODE_ACCESS || idata == nullptr) {
     return KAUTH_RESULT_DEFER;
   }
 
   auto sdm = OSDynamicCast(
       SantaDecisionManager, reinterpret_cast<OSObject *>(idata));
 
-  sdm->IncrementListenerInvocations();
-  int result = sdm->VnodeCallback(credential,
-                                  reinterpret_cast<vfs_context_t>(arg0),
-                                  reinterpret_cast<vnode_t>(arg1),
-                                  reinterpret_cast<int *>(arg3));
-  sdm->DecrementListenerInvocations();
-  return result;
+  if (action & KAUTH_VNODE_EXECUTE) {
+    sdm->IncrementListenerInvocations();
+    int result = sdm->VnodeCallback(credential,
+                                    reinterpret_cast<vfs_context_t>(arg0),
+                                    reinterpret_cast<vnode_t>(arg1),
+                                    reinterpret_cast<int *>(arg3));
+    sdm->DecrementListenerInvocations();
+    return result;
+  } else if (action & KAUTH_VNODE_WRITE_DATA) {
+    vnode_t vp = reinterpret_cast<vnode_t>(arg1);
+    if (vnode_vtype(vp) != VREG) return KAUTH_RESULT_DEFER;
+    sdm->IncrementListenerInvocations();
+    char path[MAXPATHLEN];
+    int pathlen = MAXPATHLEN;
+    vn_getpath(vp, path, &pathlen);
+    sdm->FileOpCallback(KAUTH_FILEOP_CLOSE, vp, path, nullptr);
+    sdm->DecrementListenerInvocations();
+  }
+
+  return KAUTH_RESULT_DEFER;
 }